Piezoelectric transducer



Filed Dec. 26, 1957 FIG.' .3

DIELECTRIC CONSTANT U V vooo Ozooo- 'G. N. HOWI\T1V PIEZOELECTRICTRANSDUCER 3 Sheets-Sheet 1 AGENT Feb. 13, 1962 G. N. HowATTPIEZOELECTRIC TRANSDUCER 3 Sheets-Shes*I 2 Filed DSC. 26, 1957 cuREo AT|037. 75C [|9ooF] O4 924gr. Pb F2 mugr.

.fr u, 26. wu 35 22 00 .r TZ

DIELECTRlC CONSTANT zooo nooo f 20o TEMP. c

IOO 200 TEMP. c

l/VVENTOR GLENN M HOW/47T @Y W@ 3,021,441 PIEZOELECTRIC TRANSDUCER GlennN. Howatt, Metuchen, NJ., assignorfto Gulton Industries, Inc.

Filed Dec. 26, 1957, Ser. No. 705,452 14 Claims. (Cl. 310-8) Thisapplication is a continuation-in-part of my application Serial Number698,449, tiled November 25, 1957, now abandoned.

This invention relates in general to electric circuit elements composedessentially of high dielectric crystalline materials, and, moreparticularly, to electrocoustic transducers comprising as their activeelements ceramic bodies of piezoelectric and ferroelectric crystallinematerial.

It has been found in the prior art that transducer elements comprisingpiezoelectric crystalline materials which include a high proportion oflead titanate and lead zirconate have a number of advantages over bariumtitanate transducers, in that they are operative at higher temperatures,and have more uniform characteristics over a wide temperature range.

However, in the preparation of ceramic transducer elements wh-ichcomprise va substantial proportion of lead oxide, for-variouspiezoelectric and ferroelectric applications, a' problem is created Vbythe volatilzation of lead' oxide at temperatures which are below thetiring temperatures necessary to properly mature the ceramic bodies."

This is readily apparent from the following table which gives the vaporpressures of lead oxide over the usual range of firing temperatures forthese compositions.

Table 1 Vapor pressures of Temperature lead oxide (degrees (millimeterseentigrade) of mercury)v Thus, it is apparent that at the firingtemperature of ceramic bodies of the aforesaid type including alargeproportion of lead oxide, which is 1204 degrees centigrade, the vaporpressure, interpolating from the data given in the above table, is cury.

Itis a general object of the present invention to provide improvementsin ceramic elements comprisingdielectric crystalline materials, and morespecifically, in piezoelectric and ferroelectric transducerswhichinclude ceramic bodies as theirk active elements.

A more particular object of the present invention is to providepiezoelectric and/ or 'ferroe'lectri'c" crystalline ceramic bodiescomprising a substantial proportion-ofy leadv oxide, in which thetendency of the latter ycomponent to volatilize at temperatures withinthe range of the tiring or maturing temperatures of the ceramic issubstantially reduced.

These and other objects are realized in accordance with' the presentinvention in an electrical ltransducer in which the active elementcomprises a ceramic crystalline body consisting essentially of leadoxide and one or more of the compounds, titania and zirconia, in which asubstantial amount of the lead oxide is replaced by lead liuoride` Thepreparation and specific characteristics at different about 80millimeters of mer-n 3 ,02 1,441 Patented Feb. 13, 1962 f in detail inthe specification hereinafter, with reference to the attached drawingsin which:

FIGUREy l is ashowing, in cross-section, of an electrical transducer 5tion; and n f FIGURES 2, 3, 4, 5, 6 and 7 arecharacteristic curvesshowing the temperature variations of the dielectricy constant, and theloss angle for ceramic bodies of a particular preferred composition inaccordance 'with the present invention, cured at six respectivelydifferent temperatures.

in accordance with the present inven- Referring specifically to thedrawings, the electroacoustic transducer shown in FIGURE l comprises ann electrically polarized body 1 of crystalline dielectric matey rrialconsisting essentially of a solid solution of a lead oxide, lead uoridePbFz, titanium dioxide TiOZ, and

zirconium dioxide, ZrO2. y

The following are preferred examples of mixes employed to form thesolidsolution of the present invention:

MIX I Weight, Mole grams percent PbsO4 924 9.1 PbF 1,164` 31.9 2D Tioz.316.2 26.6 ZrO;; r 595.8 32.4

` Total 3, 000,0 100. 0

. MIX II a *Weighh Mole grams percent PbO 909.0 23.0 PbF 1,173. 0 27.0Tim 318.0 22.5 ZrOz 600.0 27.5

Total y3,000.0 n 100.0

The components listed are used in their chemically cle diameters of afewmicrons, in a ball-mill, or by any other conventional means.

In the case of the foregoing mixtures, and any of the other mixtureswhich will be rset forth hereinafter, it is preferable to'precalcine thecomponents by heating them up in a closed refractory vessel. The vesselcarrying the materials to be calcined, which is of such composition thatyit does not react chemically with kthe components of the mixture at thecalcining temperature, is enclosed in a second refractory vessel inwhich is placed lead oxide, lead fluoride, lead chloride, or some othercompound of lead, or combination of lead compounds which volatilize atthe calcining temperature to produce an excess of vapor, thereofwhichapproximates the vapor pressure of the materials being calcined,thereby preventing volatilization of the lead oxide from the calcinedmixf 'Calcining is carried out 'at temperatures ranging from 1,000 to1,500 ydegrees Fahrenheit, the peak tem- ..peratures being maintainedfor periods ranging yfrom a ponents of Mix I were placed in a firstclosed rectangular vessel of hard-burned fire-clay having dimensions of11 K 1l by5 inches. .This was placed in a second closed refractoryvessel of the same material, having dimenwas placed about'2 kilograms ofP13203. `This assemblage was then heated up to 1200 degrees Fahrenheitand :maintained atl the peaktemperature for a half hour.

The' advantage of calcining `lies in the fact that it intimately tiesdown :the volatile vmaterials in the nal composition, so preventing'excessive volatilization in airsions of 14 by 14 by 8 inches, in'whichlatter container tiring of the nal parts, eliminating excessiveshrinkage, and in general making raw materials more easily processed.

After the aforesaid powder has been mixed to homogeneity and calcined,it is preformed by any of the pressing or extrusion techniqueswell-known in the art, or by combining with water and casting, or bycombining with an organic binder to form a slip which is processed inthe manner disclosed in detail in my Patent 2,486,410,

issued November 1, 1949; or alternatively, in the manner disclosed byLeslie K. Gulton in application Serial Number 615,017, tiled October 10,1956, which issued as Patent No. 2,892,955, dated June 30, 1959. Thethin sheets so processed may be cut into disks or wafers. In

accordance with the present illustration, such a wafer,

having dimensions of, for example, 3A inch length, half inch width, andabout 12 mils thick, is placed in an oven and heated from roomtemperature, at a rate of about 920 degrees Fahrenheit or 493.3 degreescentigrade per hour, to the tiring temperature.

The composition specitied may be tired at different temperatures over awide range, extending from about 760 degrees centigrade, or 1400 degreesFahrenheit, to 1065.5 degrees centigrade, 1950 degrees Fahrenheit, orhigher.

At the lower ring temperatures, the heat-treatment in the Journal of theAmerican Ceramics Society, volume 33, number 2, page 63 (1950).

The maximum tiring temperature is maintained for about one-half hour;and then the elements are allowed to cool, in the oven, to roomtemperature in about a half hour.

During the course of ring, been used in the performing vaporize, or burnon, leaving solution, into the crystal lattice any binders which haveand pressing techniques theY polycrystalline solid of which theconstituent 4 components have entered substantially in the proportionsof the mix.

lt will be apparent to those skilled in the art that the exact tiringtemperature, the tiring time, and pressure, in each case, is subject towide variations, depending on the composition employed and equipmentinvolved.

Although two particular compositions have been described by way ofillustration, a range of solidsolutions is contemplated within the scopeof the present invention, embracing proportions from about 70 molepercent PbF2, 30 mole percent PbO, to 10 mole percent PbF2, 90 molepercent PbO; the balance of the components consisting substantially ofti-tania TiOz and/ or zirconia ZrO2 in any proportionate combination.

As described in detail in the Leslie K. Gulton Patent No. 2,892,955supra, so called red lead, P11304 can be substituted, in whole or inpart, in molar ratio, for the PbO in the present combination. It is alsocontemplated that PbOz, PbO, and Pb304 can be used in variouscombinations.

Moreover, it is contemplated that in any of the foregoing solidsolutions, up to 10 percent by weight can be replaced by the addition ofoxides of cerium, lanthanurn, or niobium, or similar rare-earth oxides,titanates, zirconates, and stannates, such as barium titanate, whichserve to control the electrical characteristics of the composition, andthe position of the Curie point. Also, it will be understood that asmall percentage ot impurities is inherent in certain of thesecomponents in their commercially obtainable forms. For example,zirconiaoften includes up to two or five percent by weight of hafnium.This is not objectionablel for the purposes of the present invention.

Tables I and II list additional mixes which are suitable for thepurposes of the present invention. As shown in Table I, the lead lossesby vaporization upon tiring each of the compositions listed were noted.Those compositions including little or no 'lead' uoride showed high leadlosses.

Table I Number Firing temp. Peak temp. Remarks of moles. ring time Mix0 1. 2,200o F. (1,204.4" C) 15 minutes.. High lead loss noted.

l 2.-... ZrO2 56 Mix A ggg.-- 1,400" F. (760 0.)... --...do Very lowlead loss noted (nonmeasurable).

'2. v T02 44 Z1`O2- 55 Mix-B PbO-.. 1. 00 2,200o F. (l204.4 C.) do--High lead loss noted.

TiO2 44 ZlOz...` 56 C6024. 14

Lazos-" 14 Mix O PbO- 46 1,400o F do No measurable lead loss.

Pb FL--- 54 TiOg.-. 44 Zr02 66 0602--.. 14 148203-.. .14

Parts by Weight Firing temp. Peak temp. Remarks tiring time Mix AC75,C1.uix A; 225,1nix 1,400 F. (760 C.) l5 minutes.. Very low lead lossnoted (below experimentalerror). Mix Aon... '150.01m A; 150, -....d0. doD0,

mix C. Mix AC2 225,1nix A; 75,111ix do -do Do,

Mix A2 150,: rnx O; 150, 1,600c F. (876.65 C.) do Slightly higher leadloss noted.

IIllX Mix ABL..- 150, mix A; 150, ..-..do do Do.

mix B. Mix BC2 150, mx B; 150, ---.do do Do.

mix Mix BC3 75, mix B;225, mix l,800 I". @82.20 C.) '...-.-d0 Lead lossnoted.

Mix ABL.-- zarnix Awa mix do do D0. Mix A1 75, nx o; 225.11m do .00 D0.

Mix ABW-.- zanx A; 225.11m( 2,0000)o F. 0,098.9" do Do. Mix.no1...-.zz'mlxnamlx .-...h do D0.

Parts by weight Firing temp. Peak temp. Remarks tiring time Mix A322:5(mix O;76,nii.x 2,0000;7 F. (1,098.9 15 minutes-- Lead loss noted.vMix OBL-.. 22g'inix0;75,mix` 2,230; F. (1,204.4" do4 Highleadlossnoted.Mix 0132...-- isomxo; o, `d do D0.

m X Mix OB1 35, mix O;2,25, mix do -do D0.

Table Il the temperature of the subject transducer, in each case,

ADDITIONAL MIXES v Moles Percent by weight .47, Mix D; .53, Mix E. .46,Mix D; .54, Mix E. .45, Mix D;-.55, Mix E. .56, Mix E.

.50, Mix D; .40, ix D;

V.After the tiring andcooling treatment has been comat atmosphericpressure, from about`25 degrees centigrade to nearly 450 degreescentigrade, above the Curie point in each case, and recording, at eachstep, values of the dielectric constant, and the tangent of the lossangle.Y

These values are plotted in FIGURES 2, 3, `4, 5, 6 and. 7, the curingtemperature being indicated on the respective iigure, in each case. Thelast two FIGURES, 6 and 7 show the test results of'a body, before andafter polarization, when cured at a low tiring temperature of 760 de-rgrees centigrade (1400 ydegrees Fahrenheit). It .is apparent thatpolarization makes little diierence in the dielectric-constant and losscharacteristics, particularly in the low temperature range. i

Itis apparent that for each of the compositions the losses are veryuniform over a range extending fromV room temperature .to temperaturesabove 200 degrees centigrade. in FIGURE 5, the dielectric constant isseen to be substantially constant over a range extending from roomtemperature to above 100 degrees centigrade; and the loss tangent isnearly negligible within this range. These features are of specialinterest for numerous practical applications, in which the ceramic bodyis subject to a wide range of temperature variations.

the surfaces ofthe ceramic body 1 during the ring opi eration. Moreover,any of the conventional types of electrodes well-known in the art, suchas, for example,

evaporated electrodes of silver, platinum, -or the like, or k f coatingsof ceramic-silver, ceramic-platinum or similar f,

combinations, may beused for the purposes of the'y present invention.,

Terminals and leads 4A and 5 are respectively soldered to' oppositeelectrodes 2 and 3.

The transducer so formed is then polarized in a manner well-known in theart by heating the body up to. above j the Curie temperature, and thenallowing it to cool to a temperature below the Curie temperature,which'in `the present illustrative embodimentsis between about 250 and450 degrees centigrade.

About 330 to 150 volts per mil thickness of the ceramic body 1 is"appliedacross the terminals 3 and 4 for a period up to about an hour.Charging maystart at above the Curie point, but it.is..prefcrable 'toquench the materialto a temperature at .which there is a low loss andhigh insulation ,resistance,.at.which `point charging is applied. Thishas the advantage over charging thru the Curie point of limitingtheamount of interfacial polarization and/or. ior'imigration in thematerial,which is deleterious in nature. After polarization of therectangular wafer of the present example (which was fired at 1400 degreeFahrenheit) and after aging for a'period of about two days, thefollowing electromechanical couplingk coeiicients were measured: kL 27.7percent; kWr 24.7 percent, and kT 30.4

Such uniform behavior over a wide range of temperatures is not inherentin compositions consistingessentially of barium titanate, because oftheir much lower Curie temperatures. f

It will be apparent that elements formed in accordance with the presentinvention may be utilized in numerous different types of ferroelectricand piezoelectric applications, and for other electrical applications,such as condensers and delay lines. present Yinvention is not to beconstrued as limited to any specific` formor arrangement disclosedherein byk way of illustration, or to any of the specifically disclosedcompositions..

What I claimisf V1. An electrical circuit element comprising a ceramicbody consisting essentially of a solidV solution oflead oxide, lead,lluori de,r and -at least one crystalline :com-

pound selelcte'd from' the group consisting of titania and (zirconia,`wherein the ratiokof lead oxide to lead uoride varies overjthe range ofcombinations from substantially'30 mole percent PbO, 70 molepercent'PbF2 to percent, where the latter respectively represent thelength, f

width,` and thickness-mode vibrations. At 45 0 degrees Fahrenheit, theresistance of the body between electrodes plying a field of 60 cyclealternating current of about 3 volts per mil across the terminals 4 and5, and raising mole.. percent PbO, 10 mole percent PbF2, and wherein`the solid Vsolution of lead Voxide and lead fluoride is mole percentyand the` crystalline compound is 100 mole` percent." n f 2,.,AnVelectricalrtransducer comprising in combination a solid dielectric body,electrode means coupled to opposing surfaces of said body, wherein saidbody'consists essentially of a solid solution of lead oxide, leadfluoride, and at least Vone crystalline compound selected fromjthe groupconsisting of titania and zirconia, wherelead iiuoride 'varies over inthe ratio' oflead oxide to the range ofcombinations from substantially30 mole percent PbO, 70 mole percent PbF2 to 90 mole percent PbO, 10mole percent PbF2, and wherein the solid solution of lead oxide and leadfluoride is 100 mole percent and the crystalline compound is 100 molepercent.

3. An electrical circuit element comprising in combination a ceramicbody, and a pair of metal foil elec- Moreover, in the case of the bodyindicated f Moreover, the scope of the 7 trodes thermally bonded to saidbody, wherein said body comprises a solid solution consistingessentially of lead oxide, lead uoride, and at least one crystallinecompound selected from the group consisting of titania, and zirconia,wherein the ratio of lead oxide to lead uoride varies over the range ofcombinations from substantially 30 mole percent PbO, 70 mole percentPbF2 to 90 rnole percent PbO, mole percent PbF2, said combination oflead fluoride and lead oxide being 100 mole percent and said crystallinecompound being 100 mole percent.

4. A ceramic crystalline body which consitsts essentially of a solidsolution of lead oxide, PbO, lead Fluoride PbF2 and at least one of thecompounds titania TiO2 and Zirconia ZrO2, wherein the proportion or leadoxide to lead iiuoride varies over the range of combinations from about30 mole percent PbO, 70 mole percent PbF2, to 90 mole percent PbO, l0mole percent PbF2, wherein the lead oxide and lead fluoride together are100 rnole percent and the titania and zirconia together are 100 molepercent.

5. A solid crystalline body in accordance with claim 4 to which up to 10percent by weight has been added of at least one compound selected fromthe group consisting of barium titanate, lead titanate, lead zirconate,and oxides of cerium, lanthanum and niobium.

6. An electrical circuit element comprising in combination a dielectricbody which is a solid solution consisting of between and 35 mole percentof each of lead oxide PbO, and lead fluoride PbFE, with the balanceselected from the group consisting of one of the compounds titania andzirconia, wherein the total mole percent of the combined lead oxide andlead fluoride is equal to the total mole percent of the group consistingof one of the compounds titania and zirconia.

7. An electrical circuit element comprising a solid solution consistingof between 20 and 35 mole percent of each of the following compounds:lead oxide PbO, lead fluoride PbF2, titania TOZ, and Zirconia ZrO2y suchthat the combined mole percent of lead oxide and lead uoride is 100 andthe combined mole percent of titania and zirconia is 100.

8. A combination in accordance with claim 7 to which up to l0 percent byweight has been added of at least one compound selected from the groupconsisting of barium titanate, lead titanate, lead zirconate, andfoxidesof cerium, lanthanum and niobium.

9. An electrical circuit element comprisingin combination a ceramic bodywhich is a solid solution consisting essentially of between 20 and 35mole percent of each of lead oxide and lead liuoride with the balanceselected from the group of compounds consisting of titania and zirconia,said solution including not more than l0 percent by weight ofadulterating impurities, and a pair of electrodes coupled to said body,wherein the lead oxide and lead lluoride together are 100 mole percentand the balance from theg roup of compounds consisting of titania andzirconia is 100 mole percent.

10. A ceramic body comprising a solid solution formed from a mixconsisting essentially of about 9 mole percent Pb304, 32 mole percentPbF2, 27 mole percent Ti02, and 32 mole percent ZrOZ.

11. A ceramic body comprising a solid solution consisting essentially of23 mole percent PbO, 27 mole percent PbFZ, 22 mole percent TiO2, and 28mole percent ZIOZ.

12. A ceramic body in accordance with claim 11 in which up to about 10percent by weight of at least one compound selected from the groupconsisting of barium titanate, lead titanate, lead zirconate, and oxidesof cerium, lanthanum and niobium is added to said solid solution.

13. In forming a ceramic body consisting of a substantial proportion oflead oxide in'combination With'a compound selected from the groupconsisting of titanla and zirconia, the method of reducing the leadvapor loss which normally occurs when said body is fired to maturitywhich comprises adding to the said body amounts of lead fluoride whereinthe ratio of lead oxide to lead fluoride varies over the range ofcombinations from substantially 30 mole percent lead oxide, 70 molepercent lead uoride to 90 mole percent lead oxide, 10 mole percent leadtluoride, and wherein the total mole percent of the combined lead oxideand lead fluoride is equal to the total mole percent of the compoundselected from the group consisting of titania and zirconia, and thenfiring said body to maturity.

14. The method of forming a ceramic body which comprises a mixtureconsisting essentially of a solid solution of lead oxide PbO and leadfluoride PbFz wherein the ratio of lead oxide to lead fluoride variesover the range of combinations from substantially 30 mole percent leadoxide, mole percent lead fluoride to 90 mole percent lead oxide, 10 molepercent lead uoride, and a balance of material consisting essentially ofone of the compounds titania kand zirconia wherein the total molepercent of the combined lead oxide and lead tluoride is equal to thetotal mole percent of one of the compounds titania and zirconia, placingthe said mixture in a lirst refractory vessel which is chemically inertto the materials of said mixture, vsealing the said first refractoryvessel within a second refractory vessel in which is disposed a quantityof a material comprising at least one compound selected from the groupconsisting of the oxides and halides of lead which volatilize attemperatures within the range 1000 to 1500 degrees Fahrenheit to producean atmosphere in which the vapor pressure approximately equals the vaporpressure of the material being calcined within the said temperaturerange, heating the assemblage including said first refractory vesselwithin said second refractory vessel to a temperature within the saidtemperature range for a period of from a few minutes to several hours,cooling the said mixture to room temperature, grinding the said mixturewith a binder, processing the said mixture to form typical ceramicshapes, tiring the said shapes to maturity by heating them in an oven toa temperature ofv at least about 1400 degrees Fahrenheit for about ahalf-hour, and allowing said shapes to cool to room temperature in saidoven for about half an hour.

References Cited in the file of this patent UNITED STATES PATENTS2,424,111 Mavias July 15', 1947 2,729,757 Goodman Jan. 3, 1956 2,892,955Gulton June 30, 1959 FOREIGN PATENTS 1,062,238 France Dec. 2, 1953 OTHERREFERENCES Iale et al.: Properties of Piezoelectric Ceramics in theSolid-Solution Series Lead Titanate-Lead Zirconate- Lead Oxide: TinOxide and Lead Titanate-Lead Hafnate, J. of Research of the NationalBureau of Standards, vol. 55, No, 5, Nov. 1955, Research Paper 2626,pages 239- 254.

3. AN ELECTRICAL CIRCUIT ELEMENT COMPRISING IN COMBINATION A CERAMICBODY, AND A PAIR OF METAL FOIL ELECTRODES THERMALLY BONDED TO SAID BODY,WHEREIN SAID BODY COMPRISES A SOLID SOLUTION CONSISTING ESSENTIALLY OFLEAD OXIDE, LEAD FLUORIDE, AND AT LEAST ONE CRYSTALLINE COMPOUNDSELECTED FROM THE GROUP CONSISTING OF TITANIA, AND ZIRCONIA, WHEREIN THERATIO OF LEAD OXIDE TO LEAD FLUORIDE